Many imaging and probing applications in the infrared and visible light regions (lidar, mammography), in the UV and x-ray regions (medical imaging), and applications using ionising particles, suffer from scattering problem. Typically, scattered photons or particles which do not pass directly from the source to the object and to the detection system result in noise. This noise may greatly degrade the desired signal or image, particularly in the case of soft tissue probing by use of visible or infra-red laser light. In many applications, the image can greatly be improved by the use of a time-resolved or a time-gated detection system.
Such systems are currently complex and expensive, and currently are conceived as separate add-on units which are normally used in conjunction with conventional detectors. Gating using light, for example, is conventionally carried out using the relatively expensive device known as a pockels cell.
Similar problems apply to particle detection techniques such as slow neutron imaging. Time gating in the sub-nanosecond range, particularly with silicon detectors, can be difficult. In the x-ray range the time gate of, of example, microchannel plate devices can approach the loops range, and the best spatial resolution which can be obtained in the dimension along the line of the light without some sophisticated deconvolution technique, for example, is thus of order a few-cm. This is inadequate for most useful medical imaging techniques.
The time resolution of these gated structures is accordingly not entirely satisfactory, and generally depends upon a combination of the rise time of the gating pulse, and the response of the detector.